1. Field of the Invention
The present invention relates to a paper separation claw of a fixing apparatus in an electrophotographic image forming apparatus.
2. Description of the Related Art
In this type of fixing apparatus, while transporting recording paper sandwiched in a nip region between a pair of fixing rollers, heat and pressure are applied to the recording paper by the fixing rollers, and thus toner is fixed on the recording paper by hot-melting.
However, it is not the case that all of the toner is firmly affixed on the recording paper by melting due to this sort of fixing process; some amount of toner is transferred to the fixing rollers and affixed there because the fixing rollers have a high surface temperature. Thus, a cleaning apparatus that removes toner remaining on the fixing rollers is ordinarily provided.
A conventional cleaning apparatus removes toner remaining on the fixing rollers using blade cleaning, felt cleaning, or the like, but there is the problem that even when toner remaining on the fixing rollers is removed using such a technique, toner that is temporarily affixed to the blade or felt will return to the fixing rollers.
Consequently, a web cleaning method has been proposed. In this web cleaning method, a web sheet composed of a thin cloth is wrapped around a reel-out roller, and one end of the web sheet is connected to a reel-in roller. The web sheet is reeled out from the reel-out roller and reeled in to the reel-in roller, and during this reeling out and in the web sheet is caused to contact the fixing rollers, thus removing material affixed to the fixing rollers.
On the other hand, it may be the case that the recording paper remains wrapped around the fixing rollers after passing through the nip region and cannot be separated. Thus, as shown in FIG. 5, a separation claw 102 is provided on a fixing roller 101 surface, and the leading edge of the recording paper is peeled away from the fixing roller 101 surface by the separation claw 102. The tip of the separation claw 102 is pointed, and thus easily enters between the leading edge of the recording paper and the fixing roller 101 surface.
Also, in FIG. 5, the face of the separation claw 102 opposing the fixing roller 101 surface is flat, but it may also be the case that this face has a concave shape that follows the fixing roller 101 surface, and thus the separation claw is disposed more closely to the fixing roller 101 surface, allowing the tip of the separation claw 102 to enter between the leading edge of the recording paper and the fixing roller surface.
However, this sort of separation claw needs to be provided in the vicinity of the nip region between the fixing rollers, and so the position where the separation claw is disposed becomes upstream from the cleaning apparatus in the rotation direction of the fixing roller. Thus, the toner remaining on the fixing rollers affixes to the separation claw before being removed, and a large amount of toner affixes to the separation claw.
When this sort of paper separation claw contacts the leading edge of recording paper that has passed through the nip region, toner that has affixed to and accumulated on the separation claw affixes to the leading edge of the recording paper, and thus stains the leading edge of the recording paper.
Also, a clump of the toner remaining on the separation claw may, after becoming large, drop and be affixed to the fixing roller surface. There may be a case in which a large clump of toner on the fixing roller surface cannot be completely removed at once even by a cleaning apparatus, and catches on a peripheral component such as a thermistor for temperature detection provided along the fixing roller surface, causing damage to the peripheral component.
Accordingly, with technology disclosed in JP 2003-156967A, a heater is provided in a separation claw, the separation claw is heated, and even when toner affixes to the separation claw, this toner is immediately melted with heat and returned to the fixing roller surface. This eliminates the problem that the leading edge of the recording paper is stained and a large clump of toner affixes to the fixing roller surface, leading to damage to a peripheral component.
However, when the separation claw is heated by a heater as in the technology of above JP 2003-156967A, it is necessary to provide a sensor for detecting the temperature of the separation claw, and control the temperature of the separation claw, so an increase in the number of components and the difficulty of control are unavoidable.
Also, increased speed of the image forming apparatus is accompanied by an increase in the number of sheets of recording paper processed by the fixing apparatus, so there is an increase in the amount of heat of the fixing rollers, and the power consumption of the image forming apparatus increases to nearly the commercial AC power rating. Thus, it not preferable to have a further increase in the amount of heat due to the heater of the separation claw.